Lead-free and cadmium-free glass compositions are generally used to form glass frits which are, in turn, used to formulate glass enamel compositions. These glass/glass ceramic enamel compositions are useful for forming decorative coatings for glassware, chinaware, architectural glass and the like. They are especially useful in forming colored borders around glass sheets used for automotive windshields, sidelights, and backlights. These colored borders enhance the appearance as well as prevent UV degradation of underlying adhesives.
In general, these enamel compositions contain a glass frits, a colorant and an organic vehicle. They are applied to a desired substrate and subsequently fired to burn off the organic vehicle and fuse the frit, thus bonding the enamel coating to the substrate.
For example, automotive designs employ a black glass-ceramic enamel obscuration band around the periphery of glass windshields to hide unevenness and protect the underlying adhesive from ultraviolet degradation. Architectural, appliance, and container/dishware glass applications often include glass ceramic materials for decorative purposes.
With glass frit development there is usually a compromise involved with the final properties of the frit. In general, glass frits that have low melting ranges have average chemical durability and relatively high thermal expansions, while frits with high melting ranges have above average/excellent durability and relatively low thermal expansion. Therefore, a need exits to formulate a glass and glass enamel compositions having low firing, low expansion, and good chemical durability. Such glasses and glass enamels have been developed, which have low firing, acceptable chemical durability and reasonable expansion, but they typically require the toxic lead oxide.